Carnallite is an evaporite mineral, a hydrated potassium magnesium chloride with formula: KMgCl3.6(H2O). Carnallite usually forms in marine evaporite deposits where sea water has been concentrated and exposed to prolonged evaporation.
Carnallite precipitates with other potassium and magnesium evaporate minerals such as sylvite, kainite, picromerite, polyhalite and kieserite.
It is usually massive to fibrous with rare pseudohexagonal orthorhombic crystals. The mineral is deliquescent (absorbs moisture from the surrounding air) and specimens must be stored in an airtight container. Carnallite, being an important source of Potassium Chloride (also referred to herein as “KCl” or “Potash”), is an invaluable source for the production of synthetic fertilizers.
Carnallite may be extracted from natural brines, originating either from underground sources or from salty lakes. For example, US 2011/0123420A1 relates to a process for making carnallite.
The natural brines may precipitate the Carnallite in evaporation ponds, wherein the Carnallite is then harvested and sent to industrial plants for processing.
Further processing of the Carnallite in the plants is needed for extracting the KCl, during these processes, some of the Carnallite is dissolved resulting in side products, also known as, industrial brines. The industrial brines are usually sent back to re-precipitate Carnallite in the ponds.
However, sending back industrial brines to re-precipitate has several disadvantages as the brines are subject to seepage, their content does not fall exactly in character with the ponds brine (thus diluting the ponds solution) and they need to be re-harvested.